We Can't Find Aliens Because They're All Extinct

Alien life may well have flourished many times around our galaxy, and even our solar system. Why haven't we found it, though? It probably lived and died long before we were around, and didn't last long enough to evolve into complex multicellular forms. A new study published by scientists and researchers at the Australian National University suggests that near-universal early extinction of other lifeforms in our universe — at a cellular and microbial level — is due to the relatively rapid change of the climates on planets like Venus and Mars.

Astrobiologists Aditya Chopra and Charles H. Lineweaver, from the Planetary Science Institute and the Research School of Astronomy and Astrophysics at ANU, have released a paper saying that the lack of life on other planets — despite the ingredients for life being abundantly available — may be due to a complex interaction between the planets themselves and the life that evolves on them.

In Chopra and Lineweaver's model, which they call the Gaian bottleneck, the emergence of life on a planet is tied to its ability to evolve rapidly enough to regulate its greenhouse gas emissions, which in turn affect the albedo of the planet through the amount of frozen and liquid water and other reflective materials, which in turn affects the surface temperature.

In extremely rare cases — like on Earth — the relatively rapid evolution from single- to multicellular organisms to complex life forms did not produce enough greenhouses gases to cause runaway negative feedback and heat the planet enough to evaporate all its liquid water. It's that particular and so far unique quirk that has kept us alive, if the Gaian bottleneck explanation is accurate.

The Fermi paradox is the apparent discordance that exists between that possibility of successful multicellular life on rocky planets around the universe other than our own, and the complete lack of evidence that any life other than on Earth has existed for more than a cosmic microsecond. The traditional explanation for this is an emergence bottleneck explained by the Great Filter, but the Gaian bottleneck is an alternative that seems, at face value, to be equally likely. [Australian National University]

It's hard to quantify just how huge. Statistically we can't be the only intelligent life to have existed. There are around 100 billion planets in the milky way and there are around 10, 000 visible galaxies. To be 1/1,000,000,000,000,000 is pretty nuts.

To put it in perspective. Go to your local beach - pick up a handful of sand, each grain of sand represents one planet. In your hand you hold 400,000 planets. You need another 2,500,000,000 handfuls to see all the planets.

To put it another way, there are 100 billion planets (roughly), if 1% of that were able to create cellular life, that's 1,000,000,000 planets, if 1% of those are able to harbor multi cellular life, that's 10,000,000. If 1% of those are able to harbor complex invertebrates (or an equivalent), that's 100,000. If 1% of those are able to create stone age life, that's 1,000 planets. If 1% of those harbor industrial age life forms that's 10 planets. Finally, if 1% of those planets are space age intelligence or above, that's oh wait...0.1 planets..oh....

So yes, you are absolutely right, that we are likely not alone in the universe. However, there is an extreme possibility that we are alone in this galaxy. After all, how many extinction events has our own planet been through?

Personally, I REALLLLLLLY hope that there is a greater than 1% chance at each of those stages. However, our current data suggests perhaps not. I mean, we haven't even found 1 other planet that has the potential of a life like atmosphere.

Alternatively, there's the possibility that life evolves quite differently in different situations, and is able to become life in more than our current carbon based manner.

I don't really want to be overly critical of this information, but I have to say it seems a bit short-sighted to me. Annihilation isn't a foregone conclusion and problems like Putin and Isis etc. can be solved in the long term. Being overly negative will just breed more negativity, so let's just take a breath and try to solve these problems. Besides, I'm pretty sure the buggers have been studying us for a bloody long time. ;)

That would be included in the etc. part of my comment.
In the scheme of things, I would put Putin well above the US as an annihilation trigger. He is actively pushing the boundaries of world peace and he is more likely to be the cause of problems in the near future.

Putin's Russia is virtually surround on its borders with hostile nations armed by the US. It is hardly surprising that Putin and many of his countrymen feel substantially paranoid about this. What would the US be like if it had hostile countries armed with sophisticated weapons on its borders? The Cuban Missile Crisis in informative I think. The US is the biggest threat to our continued existence AFTER global warming.

I'm not saying the US isn't part of the problem, but most of those countries you mentioned surrounding Russia, were part of the old USSR and they opted out first chance they got for a reason. My comment was about trying to skew the dialog towards being more positive and Putin, can in no way be a positive part of the outcome. Sorry if my opinion differs from yours, but at least I can share it without fear of being thrown in a gulag or poisoned with Polonium or murdered in the street by an unexplained hit squad!

I'm pretty sure the buggers have been studying us for a bloody long time

So what is so fascinating about our arses that they need to continue probing them one after another? As you say, they've been at it a long time. You'd think by now that they'd have learned all there is to know about the human bunghole and moved on to other parts of the anatomy.

I heard (a long time ago) that the Russians picked up an SOS signal from some distant galaxy, stating that they were on the brink of destruction and it was their own fault. Did that actually happen or was that proven to be a hoax??

The way I see it, there are so many 'opportunities' for life to evolve, that statistically speaking, life out in the universe is inevitable. Sure some may die out before evolving to complex life, but all of them?? Nah, I don't think so.

I agree, the odds are in favour of another species somewhere, also we have explored next to nothing of the universe. Think it's a bit quick to go making presumptions on other life forms. I personally think there is a big galactic empire that knows about us but they have no interest in us, hence not bothering to make contact.

The Gaian bottleneck isn't an alternative to the Great Filter, which itself doesn't describe a particular event. The Great Filter is a probability threshold, and the Gaian bottleneck is one possible explanation for it, if indeed it is already behind us. There are 400 billion starts in the Milky Way alone, 1 in 20 are similar to our Sun, and latest estimates are that about 1 in 5 of those have a roughly Earth-sized rocky planet in their habitable zones. Even if the odds of life evolving to counter-act a runaway greenhouse effect are exceedingly small, that still leaves a large number of planets in our galaxy on which life could flourish. Until our telescopes our powerful enough to observe the atmospheric content of exoplanets it's all just speculation, but I suspect we'll be able to observe active methane production cycles and the IR spectra of chlorophyll-like molecules in a significant proportion of the candidate planets we investigate.

If you believe the assumption that it's not possible to travel faster than light it's not at all surprising that we haven't encountered other intelligent life. For a start, the nearest likely candidates for life are over 4 light years away. So even if they were developing at the exact same rate as us for as long, they'd be no closer to visiting us as we are them.

And that's assuming that they didn't evolve and die off 20 thousand years ago, or are currently in the equivalent of our middle ages.

I think the chances of there being *any* life somewhere in the universe must be ridiculously high. I'd even go as far as to say that it's highly likely there are advanced, intelligent beings out there. But will we ever meet them? Unlikely, unless FTL travel is developed.

The universe is so large, we are so insignificant, the visible galaxies are all within our event horizon, there are unknown structures outside the event horizon, receding from us faster than light-speed meaning that we can never know about them.

The timescale of human existence (no matter what your life philosophy is) is so short, and we have only been emitting "intelligent signals" for 100 years or so.

IF there were other intelligent lifeforms on our level, and timescale, in all likelihood our EM emissions would not yet have intersected, meaning we could know nothing about them.

If on the other hand Alien beings dwell in "dark-matter" we would know next to nothing.
What if the aliens were able to move between dark and light matter, warp space tunnel through time and control fusion, what would we call that?

Another article written from the perspective of someone who's only just picked up the topic recently and hasn't got his bearings.

Frankly, even widely respected thinkers and scientists miss the boat on this one a lot. Extraterrestrial life is a fun sandbox to play in, but that's all. Guessing that they're all dead, or that they avoid us because we're primitive, or this or that - it's all utterly stupid. It's astoundingly human-centric.

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